Electrical contact systems having spring loaded, movable contacts are employed in circuit board and electronic circuit test systems and the like in which electrical contact is made between a circuit or device and one or more test points. The electrical contact system generally comprises a metal barrel having a contact plunger telescopically slidable therein and a spring disposed within the barrel for biasing the contact plunger to a normally outward position. The contact plunger has an outer end provided with a probe tip of a selected configuration to engage a test pad or the like of a circuit board or other device. As test systems employ higher radio frequencies in testing procedures there is an increasing need to provide the shortest possible so-called electrical path in a matched impedance system. Conventional probe systems include a helical coil spring surrounding the plunger and disposed within the barrel which result in a longer than desirable electrical path. Another approach disclosed in U.S. Pat. No. 4,636,026 employs a plunger disposed within a metal sleeve having an inner end provided with angled ramp surfaces which cooperate with laterally deflectable spring fingers which serve to bias the plunger to a normally outward position.
While this device can result in a relatively short electrical path it is limited in that it has a travel range limited by the angled ramp and cannot operate over a wide range. It is further limited with regard to the diameter of the sleeve which can be used in making the device. Extended travel requires an increase in diameter of the device which in turn has an adverse effect on pitch between adjacent devices. Yet another disadvantage is that the variable geometry resulting from the changing diameter of the electrical contact on the angled ramp is inconsistent with a matched impedance system.